High dielectric material and method of making same



Patented June 18, 1946 HIGH DIELECTRIC MATERIAL AND METHOD OF MAKING SAME Eugene Wainer, Niagara Falls, N. Y., asslgnor to The Titanium Alloy Manufacturing Company, New York, 1 Y., a corporation oi Maine No Drawing.

Application November 2, 1943, Serial No. 508,743

8 Claims. (Cl. 106-46) described and claimed. The present invention relates to another group of bodies whose usefulness is equally widespread. This novel group of ceramic compositions have properties such as to make them useful as capacitors in radio, television, and communications generally, as capacitative temperature compensating devices in receivers and communication equipment to prevent distortions due to changes in circuit characteristics caused by temperature changes. The dielectric constant of some of these compositions are so high as to make possible their utilization in low frequency distribution and communication systems such as 60 cycle lines, by means of capacitative coupling between a low frequency high tension transmission line and communication telephone lines. Further, these high constants enable these materials to be used as substitutes for high capacity paper and electrolytic type condensers for by-pass, filter, and power circuits, for use in radio, fluorescent lighting circuits, etc.

Further, the very high dielectric constants make possible the use of these materials as electromechanical devices, for example, the transfer of mechanical energy or motion into electrical energy or vice versa, in a fashion similar to the action exhibited by piezoelectric crystals. Thus the novel compositions of the present invention have possible utility in pyroelectricity, supersonics, crystal or condenser microphones, frequency stabilizers, loud speakers, phonograph pickups, telephone design, and oscillator designs generally. The foregoing remarks apply particularly to those bodies whose dielectric constants are over 1000 at radio frequency. In condenser microphones, very thin sheets of the higher dielectric constant materials are rigidly clamped at either center or edges and used as vibrating diaphragms. The minute changes of dimension or position of the dielectric due to vibration will occasion relatively large changes in capacity by means of which sound is transformed into electrical energy.

Other members of this group, particularly those having dielectric constants over 1000 appear to exhibit electrical and mechanical characteristics of the same nature as piezoelectrical and pyroelectrical crystals. For example, a rod of the material having one end fixed and one end free to vibrate will develop a potential difference of several volts between the two ends of the rod, when in vibration.

The particular usefulness of this group as compensators for correction of frequency drift lies not only in the possibility of obtention of both positive and negative temperature coeflicient of a wide variety but also the possibility of controlling the variation through choice of the proper composition. Furthermore, some of the temperature coefficients make members of the group useful as mica substitutes, particularly because of the low power factors available.

These novel compositions consist broadly of fired mixtures of the titanates of the alkaline earths with the zirconates of the alkaline earths. Mixtures of alkaline earth titanates, stannates, and zirconates are also of utility. The alkaline earth compounds generally are of utility for this invention, including those of magnesium, calcium, strontium and barium. The peculiarly beneficial effect of the zirconate additions is most strikingly shown in the case of additions to BaTiO'a. At radio frequencies barium titanate has a dielectric constant of 1200-1300, and a temperature coefiicient which is first negative, then strongly positive, and finally strongly negative between 20 and C. Not only may this erratic behavior be eliminated by addition of the zirconates to barium titanate but dielectric constants of the order of several thousand are common.

In the practice of the present invention, the ingredients as indicated in the table below are properly reacted ceramically and then ground so that the coarsest particles will pass a 325 mesh screen. The dried powders are then mixed within the limits indicated by the proportions given in the table. Approximately 10% water is added and thoroughly mixed in the damp powder, granulated by passage through a 20 mesh screen. They are then pressed in a die under a pressure of 5 to 10 tons per square inch, and then allowed to air dry for 24 hours. The pieces used for the purposes of this specification are roughly 1 inch in diameter and 0.1 inch thick. Pieces of such size are fired-on a schedule of 400 F. per hour to the peak temperature, then held at peak temperature for three hours, and then allowed to mwmmmmmwwmmwm hich is 3 cool. The maturation temperature !or all the bodies listed below is between 2450' F. and 2500' 1''. After cooling, the opposing parallel surfaces are painted with silver powder paste w fixed as a silver electrode by firing to 1500' F. The values obtained below were determined at one megacycle, using a radio frequency bridge of standard design. Resistivity was determined on a high sensitivity resistance circuit on which a resistance oi a million megohms could easily be detected, the :rero point indicator being a galvanometer. The 1000 cycle measurements were obtained through use or an impedance bridge of standard design, whose arms were resistive components.

The temperature coefllcients of the compositions listed are indicative of the scope of varia- Whlle single compositions may yield the desired coemcient, an infinite variety of coeillcient is possible through parallel combination of one or more bodies.

What is claimed is:

1. A dielectric composition substantially consisting of barium titanate and an alkaline earth zirconate, the latter being present in an amount less than parts for each 100 parts of the iormer combined ceramically whereby the dielectric properties of barium titanate are regulated.

2. A dielectric composition substantially consisting of barium titanate and calcium zirconate,

the latter being present in an amount less than 20 parts for each 100 parts or the former combined ceramically whereby the dielectric properties of barium titanate are regulated.

tion possible.

Power iactor percent 3. A dielectric composition substantially consisting oi barium titanate and strontium zirconate, the latter being present in an amount less than 20 parts for each 100 parts of the former combined ceramically whereby the dielectric properties of barium titanate are regulated. do 4. A dielectric composition substantially consisting of barium titanate and barium zirconate, the latter being present in an amount less than 20 parts for each 100 parts oi the former combined ceramically whereby the dielectric properties of barium titanate are regulated.

5. The method of regulating the dielectric properties 0! barium titanate which comprises combining barium titanate ceramically with a 12222l2200000000ll2224a minor amount of an alkaline earth metal zinconate.

6. The method of regulating the dielectric properties of barium titanate which comprises combining barium titanate ceramically with a minor amount oi! calcium zirconate.

wmmmmwmmmmmmm One kitocycle Dielectric constant LLZaJ LLoNB ZO- ZZZZQLLLLI III that not only may The possibility of Power iactor percent Table 1 One megaeycle M 2222222222222 w wmmmmmmmmmmmm B 22 2.oa t222 m mmmmmmmmmwmmm B 22222a2a2m222 m mmwwwwmmmwwwm B 1111111111111 m mmmmmmmmmmmwm n 2222232222222 m mmmmmmmwmmmmm B LLI LLLLLI LLLL The data below indicate filter, and power pack condensers as substitutes for paper and electrolytics but also as substitutes for mica both from standpoint of power factor 20 these groups of compositions be used for by-pass,

and temperature coemcient. variation and control 01' temperature coeihcients is indicated from Table 2. These data were obtained at one megacycle.

6 m mmwmmmmmmmmwmwmwmmmmmwm Mm LLZB LLZ ZZZ ZZZZQMZLLLLLLI W a U m m m if; M a r m {0L 6 1357111 a W mmmmm B s M r M I m a nmmmmnm Table 2.--Temperature coemcient of capacity Temp., "C.

EUGENE WAINER. 

